Brewing unit for automatic coffee machines

ABSTRACT

The present invention relates to a brewing unit for a coffee machine. The brewing unit comprises a brewing chamber in which a dose of coffee powder can be put, an inlet for supplying water to the chamber for preparing a coffee beverage, a first piston providing a moveable wall for adjusting the chamber internal volume, which wall has an outlet connected to a spout for delivering the coffee beverage to the user, and a valve assembly for connecting said spout to the brewing chamber or the atmosphere according to the position of the supporting means. Advantageously a second piston is provided which moves the first piston and supports the valve assembly. The second piston is also moveable with respect to the first piston, for actuating the valve assembly.

The present invention relates to an improved brewing unit for coffeemachines. In particular the invention relates to automatic coffeemachines for beverage dispensing, e.g. the so called HoReCa machines.These machines are provided with brewing units including a brewingchamber having a filter element where coffee powder is fed and usuallycompressed. Hot water is then fed to the chamber for brewing the coffeepowder, thereby preparing the coffee beverage which is delivered,through the filter element, to the user.

It is known to provide brewing units with valve assemblies forregulating the outflow of the coffee beverage delivered from the brewingchamber.

WO 02/091889, in the name of DE LONGHI, discloses a filter-holding cupfor a coffee machine. The filter-holding cup coupled to the relatedmachine defines a brewing chamber. The cup comprises a spring biasedvalve arranged downstream from the filter. Most of the time the valvebody is kept in a closing position by the spring. Only during operationof the machine, the coffee beverage exiting the filter impinges thevalve body against the bias force of the spring, thereby causing thevalve body to move axially in an opening position.

In the aforesaid or similar solutions, the coffee flow valve, which isarranged downstream from the brewing chamber, is wetted by the coffeebeverage exiting the brewing chamber at each dispensing cycle of themachine.

Residues of the coffee beverage have adhesive properties and build up onthe valve seat and the valve body surfaces, acting as a “glue” andeventually causing jamming of the valve body within its seat.

This problem occurs in particular in brewing units wherein the valvebody is made of (or covered with) a plastic material, for instancesilicone or a similar thermoplastic material. Such material, when soiledby the coffee delivered from the brewing chamber, easily adheres to theseat, thereby keeping the valve assembly in a closed position.

In order to avoid jamming of the valve assembly, the valve body is oftenremoved by the final user of the coffee machine or the maintenanceoperator.

In other words, prior art coffee machines affected by the aforesaidproblem are often tampered for removal of the valve body. Therefore,operation of the coffee machines changes with respect to the parameterspreset by the manufacturer and the quality of the delivered coffee islowered. In fact “espresso” coffee is usually prepared by brewing in achamber substantially closed, while “americano” coffee is prepared bybrewing in a chamber having its exit open.

U.S. Pat. No. 6,382,083, in the name of SCHMED, discloses a brewing unitfor coffee machines provided with a valve assembly inserted between thebrewing chamber and the beverage outlet in order to control the flowrate of the coffee beverage. The valve assembly comprises a valve bodymember movable against the force of a spring between a first position,wherein the valve body does not close the seat but leaves a minimum gap,and a second position, wherein the valve body still does not close theseat and leaves the maximum gap. The spring is set to keep the valvebody member in the open position.

By adjusting the bias force of the spring, the user changes theextension of the gap between the valve body and the related seat, thiscausing changes in the amount of coffee to be brewed per time unit.Italian patent IT 1142041, in the name of GROSSI, discloses a brewingunit wherein a valve is positioned in a passage provided in the filterelement for regulating the outflow of the coffee beverage prepared inthe brewing chamber. This valve has a valve body which is axiallymovable and has size and the shape such that, during preparation of thecoffee beverage, it does not close the outlet passage of the filterelement but leaves an annular gap. Presence of such annulus gap shouldprevent malfunctioning of the brewing unit due to clogging of the filterelement.

Brewing units similar to those disclosed in U.S. Pat. No. 6,382,083 andIT 1142041, do not allow for closing the valve and relevant pressurebuild-up within the brewing chamber to e.g. prepare an espresso coffee.

Thus, there is the need for a brewing unit which allows for closing ofthe valve assembly downstream from the brewing chamber and, at the sametime, prevents jamming of the valve body.

It is an object of the present invention to provide a brewing unit forcoffee machines which overcomes the drawbacks of known solutions, beingat the same time easy to manufacture and assemble and inexpensive.

It is still an object of the present invention to provide an easy tooperate brewing unit for coffee machines which avoids jamming orclogging of the coffee outlet valve assembly.

It is another object of the present invention to provide a brewing unitfor coffee machines which overcomes the drawbacks related to soiling ofthe valve assembly arranged downstream from the brewing chamber, beingat the same time easy to clean.

These and other objects are achieved by the present invention whichrelates to a brewing unit according to claim 1.

Advantageously the brewing unit according to the present inventionprevents adhering of the valve to the surfaces of the related seat, inthe delivery outlet.

The second piston, which supports the first piston and the valveassembly, remains in the first position when the brewing unit is notoperating. In other words the first position of the second piston isalso its starting position for the operation and corresponds to thevalve assembly being spaced and separate from the delivery outlet. Inthis way the valve assembly, and in particular the valve body, is notsubject to adhesion to the delivery outlet surfaces due to the effect ofthe coffee residues, nor is it affected by building up of residues nextto the valve assembly.

Preferably the second piston and the first piston are arranged coaxiallyand are moveable along the same axis, for instance sliding withinguides. The second piston is actuated by any suitable device, forexample a motorized endless screw engaging a guide of the same piston.

The stroke of the second piston is transmitted to the first piston forpushing its end portion, which comprises the aforesaid wall, against thecoffee powder contained into the brewing chamber. The moveable wallcompresses the coffee powder to the desired level.

The first piston and the second piston are coupled by means of one ormore resilient elements, such as springs. The resilient elements aredesigned to resist a preset threshold compression force withoutdeforming and to be themselves compressed if the force exceeds suchthreshold.

When the first piston has compressed the coffee powder to the desiredlevel of pressure, and the second piston still forwards toward the firstpiston, the resilient elements yield, thereby allowing the second pistonto bring the valve assembly into contact with the delivery outletsurfaces, so as to close the same. Movement of the second pistonbackward, toward its first position, causes the resilient elements toreturn to their initial extension, while the first piston is still,thereby separating the valve assembly from the delivery outlet, so as toopen the same. Further backward movement of the second piston istransmitted to the first piston by the extended resilient elements andthe same first piston is moved a correspondent distance from thecompressed coffee powder.

The brewing unit according to the present invention permits to prepareboth “espresso” coffee beverages and “americano” coffee beverages.

An “espresso” coffee beverage can be prepared by operating the brewingunit to comprise the following steps:

-   -   providing a dose of coffee powder into the brewing chamber;    -   moving the second piston from its starting first position toward        the brewing chamber to push the first piston (its moveable wall)        against the coffee powder to achieve desired compression of the        same;    -   moving the second piston toward the first piston, i.e. applying        a relative motion of the second piston with respect to the first        piston, until the second piston reaches the second position,        thereby closing the delivery outlet with by way of the valve        assembly;    -   supplying water to the brewing chamber; and    -   moving the valve away from the delivery outlet, thereby opening        the same and allowing the coffee beverage to exit the brewing        chamber once a sufficient pressure is reached in the brewing        chamber.

An “americano” coffee beverage can be prepared by operating the brewingunit to comprise the following steps:

-   -   providing a dose of coffee powder into the brewing chamber;    -   moving the second piston from its starting first position toward        the brewing chamber to push the first piston against the coffee        powder to achieve the desired compression of the same;    -   moving the second piston back to leave a gap between the valve        body and the valve seat and between the compressed coffee and        the movable wall;    -   supplying water to the brewing chamber while keeping the        delivery outlet open, thereby allowing the coffee beverage to        exit the brewing chamber.

The valve assembly always remains in an open configuration when thebrewing unit is in stand-by, i.e. when the unit is not operative. Inthis way the valve body cannot adhere to the surfaces of the deliveryoutlet, thereby overcoming the adhesion effect of the coffee residues.

The valve body contacts the surfaces of the delivery outlet when thebrewing unit is operated for delivering an “espresso” coffee, but onlyfor a time necessary for the preparation process or for a time pre-set.

In other words, according to a first embodiment, the valve can remainclosed upon action of a spring having a closing force that is less thanthe force of the beverage pressure within the brewing chamber: once asufficient pressure is reached, the valve is opened against the springforce.

According to a second embodiment, the valve is open by moving the secondpiston—and the valve mounted on it—away from first piston, that remainsstill, i.e. that does not move with respect to the brewing chamber.

According to third embodiment, the valve is opened by an actuator knownin the art that operates the valve after a pre-set time has lapsed.Suitable actuators are e.g. electromagnets, or similar elements, actingon the valve body.

When the brewing unit is operated for delivering an “Americano” coffee,the valve body may contact the delivery outlet surfaces for a short timelapse because of the movement of the second piston pushing the firstpiston for compressing the coffee powder, but the same valve is removedfrom the outlet when the second piston is withdrawn before brewing ofthe coffee powder.

Alternatively, the valve is opened by command of an actuator, that isoperated by the machine control unit to provide a brewing chamber withcoffee compressed between two pistons and having a brewing chamber openoutlet.

The brewing unit according to the present invention is compatible withcommon coffee machines. In particular, the brewing unit of the inventioncan be installed in automatic coffee machines for home or office use, orto be installed in food-service sites or in so called HoReCa(Hotel-Restaurant-Café) sites or, still, in public areas. Since thebrewing unit overcomes jamming of the valve assembly at the exit of thebrewing chamber, maintenance of the related coffee machines is simplerwith respect to machines provided with prior art units, with evidentadvantages for what concerns the operating costs.

A further advantage of the presence of an actuator for opening the valveby command, is that the brewing time can be accurately controlled toincrease the quality of the beverage.

Further advantages and features of the present invention will becomeapparent from the following detailed description with reference to thedrawings enclosed as a non-restrictive example, where:

FIG. 1 is a perspective view of a brewing unit according to the presentinvention;

FIG. 2 is a cross section view along line A-A of FIG. 1;

FIG. 3 is a cross section view along line B-B of FIG. 1;

FIGS. 4 and 5 are enlarged views of the valve assembly in the open andclosed conditions;

FIG. 6 shows a valve assembly provided with a valve actuator to open orclose the valve when required.

With reference to FIG. 1, the brewing unit 1 according to the presentinvention comprises a brewing chamber 2, having a top wall 3 and abottom wall 16; top wall 3 is moveable to adjust the chamber internalvolume. The brewing chamber is intended to house a dose of coffee powdersupplied, through the chute 4, by an external unit, for instance agrinding unit of the coffee machine (not shown).

Moveable wall 3 is normally including a filter (not shown) and is aportion of a first piston 5 which is arranged to move with respect tothe brewing chamber 2 so as to press the coffee powder contained thereinand close the chamber 2 during the brewing process.

An outlet 12 for the brewed coffee is provided through the wall 3. Theoutlet 12 is a through hole usually connected to a plurality of recessesprovided on the surface of wall 3, under the filter, to collect thebeverage.

The first piston 5 has a generic cylindrical shape to match the shape ofthe brewing chamber 2 and moves along the axis X shown in FIG. 2 toopen/close the chamber and press the coffee powder. The first piston 5is moved along the axis X by a second piston 6 to which piston 5 iscoupled by coupling means that allow to move first piston 5 with respectto second piston 6.

In the embodiment shown in FIGS. 2-3, the coupling means are resilientelements 7, preferably a couple of springs.

A portion of the second piston 6 is slidingly inserted into first piston5 so as to leave a gap 15 between the wall 3 of the first piston 5 andthe lower external surface of the same second piston 6 when the unit isnot in use.

A valve assembly 13 is provided on second piston 6 and is movable withit along axis X-X and with respect to first piston 5. Valve 13 ispositioned at the gap 15 between the first piston 5 and the secondpiston 6 for opening and closing the delivery outlet 13 of the wall 3.

Preferably the valve assembly 13 comprises a spring biased valve body14.

Such valve body 14 is shaped to match with the surfaces defining thedelivery outlet 12. In the embodiment shown in the figures, valve body14 is made of or comprises a covering of silicone or other similarmaterial. The valve body 14 is intended to be able to close deliveryoutlet 12 by abutting the facing internal surface of wall 13. The valvebody can be more or less deformable under pressure; in one embodiment,valve body 14 can be deformed by the brewed coffee pressure withinchamber 2 and let out coffee upon being deformed. Preferably, the valvebody will withstand the pressure in the brewing chamber withoutdeforming; opening the outlet is obtained by compression of spring 20(see FIGS. 4 and 5).

The second piston 6 is arranged coaxial with the first piston 5 and iscoupled to an actuating device controlled by the related coffee machine.It is understood that the actuating device can be any suitable knowndevice for imparting the movement to the second piston 6 along the axisX-X.

In the embodiment shown in the figures, the actuating device comprisesan endless screw 8, engaging an element 9 jointed to the second piston6, and a guide 10 also engaging in a slidable way the element 9. Theendless screw 8 is rotated by a gear 11 controlled by the coffee machinecontrol unit. Rotation of the endless screw 8 causes the rotation of aplurality of gears 8′ that rotates a second endless screw 8″ so thatsecond piston 6 is translated a correspondent stroke along the axis X.

Bottom wall 16 can be moved within chamber 2 in a similar way bycorresponding gears and screws (FIG. 2).

In FIGS. 1-3 the second piston 6 is shown in its first position, whichcorresponds to piston 6 being raised upon the brewing chamber 2 asufficient distance to keep the wall 3 of the first piston 5 far fromthe brewing chamber 2, so as not to close the same chamber. When thesecond piston 6 is in this first position a dose of coffee powder can bedropped into the brewing chamber 2.

Operation of the brewing unit 1 will be explained in the following withreference to the preparation of an “espresso” coffee beverage.

Once the coffee powder is supplied into the brewing chamber 2, thesecond piston 6 is moved, by endless screws 8, 8″ and gears 8′, from itsinitial first position along the axis X, toward the same brewing chamber2. The first piston 5 moves with the second piston 6 so as to bring thewall 3 against the coffee powder and achieve the desired pressing of thesame powder.

The first piston 5 is pressed against the coffee powder until theresilient elements, i.e. the springs 7, are compressed between the firstpiston 5 and the second piston 6. When the springs 7 yield, the firstpiston 5 remains still, while abutting the pressed coffee pastillewithin the chamber 2, and the second piston 6 moves forward, toward thechamber, thereby reducing the gap 15. This position is shown in FIG. 4.

Further movement downwards of the second piston 6 against the firstpiston 5 causes the valve assembly 13 to operate, i.e. the second piston6 moves into a second position at which the valve body 14 closes thedelivery outlet 12, as shown in FIG. 5.

In this configuration, the coffee powder is pressed within the brewingchamber 2 and the valve body 14 of valve assembly 13 closes the outlet12.

Water is fed to the brewing chamber through a suitable channel (notshown) provided on the wall 16 opposite to the wall 3.

Delivery of the brewed coffee from the brewing chamber 2 by opening ofthe outlet 12, can be obtained in different possible ways. In oneembodiment, opening 12 is opened because the pressure of the liquid inchamber 2 is greater than the force of spring 20 that biases valve body14 away from valve assembly 13.

In another embodiment, valve assembly is operated by an actuator such asan electromagnet.

In other embodiments, outlet 12 is opened by moving piston 6 upwards,i.e. away from piston 5.

In one of these further embodiments, once brewing of the coffee has beencarried out, this usually occurring in a preset time lapse, the secondpiston 6 is moved backward by a counter-rotation of the endless screws8, 8′, thereby releasing springs 7 from compression and maximizing gap15. This causes the valve assembly 13 to open the delivery outlet 12.The coffee beverage exits the brewing chamber 2 and is channelled towardthe spout 17 for delivering to the user.

FIG. 6 shows a further embodiment wherein in lieu of springs 7 arotating gear 21, operated by screw 22, is provided on piston 5 and ismeshing with teeth provided on piston 6. In this embodiment, the volumeof brewing chamber 2 can be kept constant because the screws 8, 8″ arenot operated while screw 22 is rotated to operate gear 21. In this way,wall 3 will not move while piston 6 is moved away from it to open outlet12. Accordingly, piston 5 can thus remain in a position of “coffeecompressed” and valve 13 can be opened to give a coffee as resultingfrom a mix of espresso and americano steps (i.e. compressed coffee andopen outlet).

After the coffee has been delivered, second piston 6 is furtherwithdrawn toward its first position (FIG. 3), so that the brewing unitis ready for another preparation cycle. The springs 7 are now completelyextended and the first piston 5 has been lifted together with the secondpiston 6.

Discharge of the residual coffee pastille is achieved by raising thewall 16, which is also moveable in a manner known per se, to be flushwith the surface 18. A motorized arm 19 is operated and pushes theresidual pastille toward a discharge. The wall 16 is lowered in positionfor another preparation cycle.

The skilled person will appreciate that when the brewing unit 1 is notoperating, the valve body 14 is not in contact with the delivery outletsurfaces. Adhering of the valve body 14 to such surfaces is thusprevented, and maintenance of the brewing unit 1 results simpler withrespect to prior art units.

Operation of the brewing unit 1 will be explained in the following withreference to the preparation of an “americano” coffee beverage.

Once the coffee powder is supplied into the brewing chamber 2, thesecond piston 6 is moved with the first piston 5, by the rotatingendless screws 8, 8″ from its initial first position to the brewingchamber 2. The wall 3 of the first piston 5 can either close the brewingchamber 2 without pressing the coffee powder, thereby stopping adistance from the powder, or press the powder and being moved back alength sufficient to leave a gap between the powder and the same wall 3.In both cases the internal volume of the brewing chamber 2 is adjustedto be greater than the volume of the same chamber 2 when an espressocoffee is prepared. It is understood that the valve body 14 does notclose the delivery outlet 12 during the brewing process, i.e. when wateris supplied into the chamber 2. The coffee exits the chamber through theopen outlet 12 and is channelled to the spout 17 for delivery to theuser.

The residual coffee powder is discharged as previously mentioned.

The first position of the second piston 6 is such that the valveassembly 13, coupled to the first piston 5, stands separate from thedelivery outlet surfaces during the stand-by of the brewing unit. Thisallows for minimizing the build up of hard residues at the outlet 12 andthe valve body 14. The coffee beverages exiting the chamber 2 providecleaning of the outlet 12 and the valve body 14 from soft residues.

The brewing unit 1 is simple to manufacture and inexpensive. The pistons5 and 6 can be made of a thermoplastic material, for instance ABSplastic. The same pistons 5 and 6 are shaped so as to allow easycoupling and disassembly, thereby promoting easy cleaning of suchcomponents from residues.

The invention claimed is:
 1. A brewing unit (1) for a beverage preparingmachine comprising: a brewing chamber (2), a first piston (5) providinga mobile wall (3) of said chamber, said mobile wall (3) having an outlet(12) and a spout (17) for delivering the beverage from said brewingchamber (2), and a valve assembly (13), and means (6) for supportingsaid piston (5) and said valve assembly (13), said supporting means (6)being movable with said first piston (5) with respect to said brewingchamber (2) and being also movable with said valve assembly (13) withrespect to said first piston (5), for actuating said valve assembly (13)to respectively connect said spout (17) to said brewing chamber (2) orto the atmosphere, according to the position of said supporting means(6).
 2. The brewing unit according to claim 1, wherein said supportingmeans is a second piston (6) coaxial with and partially housed in saidfirst piston (5).
 3. The brewing unit according to claim 2, wherein saidvalve assembly (13) is mounted on an end wall of said second piston (6)overlying said moveable wall (3) of the first piston.
 4. The brewingunit according to claim 3, wherein said first piston (5) and said secondpiston (6) are moveable along a common axis (X) and a portion of saidsecond piston comprising said end wall is movable, along said axis, in aportion of said first piston comprising said moveable wall.
 5. Thebrewing unit according to claim 2, wherein said first piston (5) andsaid second piston (6) are biased in a spaced position by means ofresilient means.
 6. The brewing unit according to claim 4, wherein saidvalve assembly (13) comprises a spring (20) biased valve body (14)arranged parallel to said common axis (X) of movement of said pistons.7. The brewing unit according to claim 2, wherein when said valveassembly is provided with actuating means (21, 22) located on said firstpiston.
 8. The brewing unit according to claim 7, wherein said actuatingmeans comprises gear means (21) connected to teeth provided on saidsecond piston (6) to move said second piston with respect to said firstpiston (5).
 9. The brewing unit according to claim 4, wherein saidsecond piston is moved along said common axis by an actuating device.10. An apparatus for preparing a brewed beverage, comprising a beveragepreparing and dispensing machine having a brewing unit (1) that includesa brewing chamber (2), a first piston (5) providing a mobile wall (3) ofsaid chamber, said mobile wall (3) having an outlet (12) and a spout(17) for delivering the beverage from said brewing chamber (2), and avalve assembly (13), and means (6) for supporting said piston (5) andsaid valve assembly (13), said supporting means (6) being movable withsaid first piston (5) with respect to said brewing chamber (2) and beingalso movable with said valve assembly (13) with respect to said firstpiston (5), for actuating said valve assembly (13) to respectivelyconnect said spout (17) to said brewing chamber (2) or to theatmosphere, according to the position of said supporting means (6).